The central role of macrophages in both innate and acquired immune responses has been appreciated for some time. It has recently become clear that such immune responses also play key roles in the regulation of macrophage activation and function, through engagement of macrophage receptors for complement activation products, chemokines, pro- and anti-inflammatory cytokines, immunoglobulins, and ligands on activated T cells. Further, it is becoming evident that dysregulation of pathogen-mediated subversion of macrophage activation and function is critical to pathogenesis in diseases as varied as sepsis, measles, leishmaniasis, AIDS, asthma, and organ-specific autoimmune diseases. The understanding of the molecular basis for the regulation of macrophage activation and effector mechanisms has made rapid progress in recent years. No meeting has taken advantage of this recent explosion in knowledge. The goal of this meeting is thus to review the state of knowledge of the bi-directional effects of macrophage activation and deactivation on innate and acquired immune responses. The current ferment in the field is, in many ways, outside the classical preoccupations of macrophage biology. By bringing together a critical mass of multidisciplinary researchers, this symposium should provide an ideal forum both for the in-depth exposure of junior investigators (graduate students and post-docs) to a fast-moving, fruitful area of immunobiological research, as well as for enticing such scientists into the field. The symposium is being held in conjunction with one on "Interfaces between Innate and Adaptive Immunity."